Side rolling tarpaulin systems, such as that described and illustrated in Ellingson U.S. Pat. No. 4,691,957 issued Sept. 8, 1987 have proven desirable for use in providing waterproof coverings for open tops of truck trailers. Such tarpaulin systems comprise an elongated tarpaulin, with a longitudinal edge fixed to one side of the trailer. A roll bar is secured to the free edge of the tarpaulin and is rotated with a crank rod to roll the tarp over rigid transverse support members secured across the open top of the truck, to an enclosing position with that free edge positioned over and secured to the other side of the trailer.
One problem with such a system is that the transverse tarpaulin support members can be removed only with difficulty, usually requiring the operator of the truck to ascend to the tops of the walls of the trailer to physically remove these members. (Removal is often necessary when the trailer is being loaded from the top, a common occurrence with such open top truck trailers.) Cramaro U.S. Pat. No. 4,915,439 issued Apr. 10, 1990 provides an attempt to solve this problem by providing for the pivoting of these rigid transverse supports about one end out of position to clear the open top. Such a system is still relatively awkward to operate, requiring the operator to individually rotate each of the transverse members into and out of loading position clear of the top opening of the trailer. As well, the transverse members are not as securely held in transverse position, as otherwise would have been the case, since they must be readily releasable, from one end, to enable them to be pivoted out of transverse position when required.
Biancale U.S. Pat. No. 4,281,872 issued Aug. 4, 1981, Cramaro Canadian Patent No. 995,714 and U.S. Pat. No. 4,858,984 of Weaver issued Aug. 22, 1989 teach longitudinally retractable tarpaulin systems for truck trailers in which a series of transverse bows, are secured to the tarpaulin extending across the top of an open trailer, and have their ends secured to a single movable cable or a pair of movable cables. The tarpaulin system, supported on the bows, is secured to each of the bows. Movement of the cable or cables causes longitudinal movement of the bows and hence tarpaulin, to retract it into open position or to move it to closed position covering the top. Such a system is not practical with a side rolling tarpaulin, however since the tarpaulin must be secured to each of the movable bows for it to operate properly.
It is an object of the present invention to provide a side rolling tarpaulin system in which the open top of the trailer or truck box may be more easily cleared for loading or unloading, and in which the tarpaulin system may then be more easily closed to cover the top.